Brain ¹⁸F-fluorodeoxyglucose positron emission tomography: An efficient tool at the initial diagnosis of nonlesional...

This study evaluates the diagnostic performance and prognostic value of brain ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) at the initial diagnosis of patients with nonlesional late onset epilepsy (NLLOE).

In this cohort study at the University Hospital of Nancy, France, newly diagnosed NLLOE patients, >50 years old, were consecutively included from June 2017 to January 2021 and systematically underwent brain ¹⁸F-FDG PET. They were categorized into four presumed etiological NLLOE subtypes: neurodegenerative subtype (NDS; patients with a diagnosis of neurodegenerative disease), microvascular subtype (MVS; patients with ≥3 cardiovascular risk factors and ≥2 vascular lesions on magnetic resonance imaging), inflammatory subtype (IFS; patients meeting international criteria for encephalitis), and unlabeled subtype (ULS). A systematic patient follow-up (at least 2 years) allowed assessment of cognitive outcomes under antiseizure medication by comparing for each patient the proportion of preserved/altered scores between initial and second neuropsychological assessment. Brain ¹⁸F-FDG PET was analyzed using a combined visual and semiquantitative approach at the individual level.

Eighty-seven patients were included (NDS, n = 18; MVS, n = 22; IFS, n = 7; ULS, n = 40). A normal ¹⁸F-FDG PET was observed in 46% of patients, with the final diagnosis of 88% of these patients excluding a neurodegenerative or inflammatory disorder. ¹⁸F-FDG PET had a negative predictive value of 94% for a cognitive decline at follow-up, similar for the overall population (n = 71) and the ULS population (n = 32). Moreover, a PET hypometabolic pattern suggestive of a neurodegenerative disorder was indicative of cognitive decline at follow-up in 74% of cases.

¹⁸F-FDG PET as part of the initial diagnosis of NLLOE patients may have a significant impact on both NLLOE diagnosis and cognitive prognosis. For almost half of NLLOE patients, a normal ¹⁸F-FDG PET could help to exclude neurodegenerative and inflammatory epilepsy etiologies as well as future cognitive decline.